Previously the renderer checked a process-wide command-line switch to
decide whether to create a Node.js environment for dedicated workers.
When a renderer process hosted multiple WebContents with different
nodeIntegrationInWorker values (e.g. via window.open with overridden
webPreferences in setWindowOpenHandler), all workers in the process
used whichever value the first WebContents set on the command line.

Instead, plumb the flag through blink's WorkerSettings at worker
creation time, copying it from the initiating frame's WebPreferences.
The check on the worker thread then reads the per-worker value. Nested
workers inherit the flag from their parent worker via
WorkerSettings::Copy.

The --node-integration-in-worker command-line switch is removed as it
is no longer consumed.